JP2007290904A - Silica particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide silica particles which do not aggregate and can be easily dispersed in a resin even if they are stored for a long term and show no decrease in flow property as powder. <P>SOLUTION: The silica particles are characterized in that when an FT-IR spectrum is measured in a dried state by a diffuse reflection method and the maximum absorbance of 1,000-1,050 cm<SP>-1</SP>and the maximum absorbance of 3,640-3,690 cm<SP>-1</SP>are defined as A<SB>S</SB>and A<SB>O</SB>, respectively, the value of A<SB>O</SB>/A<SB>S</SB>is within a range of 0.04-0.7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to silica particles, particularly silica particles suitable for a spacer of a liquid crystal display panel.

  In recent years, liquid crystal displays have been increasing in size and definition, and liquid crystal display elements have been improved in terms of high-speed response, high contrast, viewing angle, etc. It has become. Therefore, a spacer is used to keep the glass substrate interval (cell gap) of the liquid crystal display panel constant.

  The spacer includes an in-plane spacer used for a display portion of a liquid crystal display and a seal spacer used by mixing with a sealing material for sealing liquid crystal.

  Glass fiber rods (for example, see Patent Document 1) and synthetic resin spherical spacers (for example, see Patent Document 2) have been used as seal spacers. Synthetic resin spacers have dimensional accuracy. In addition to being very high, it has a problem that it is difficult to use for a high-quality liquid crystal display because it deforms when compressed. On the other hand, although the glass fiber rod has high dimensional accuracy, the end of the rod is sharp, and thus there is a risk of damaging an electrode, an alignment film, a color filter, and the like formed on the glass substrate.

  From such a point of view, it has been proposed and used to use true spherical microspheres formed by hydrolysis and dehydration condensation polymerization of metal alkoxides as seal spacers (see, for example, Patent Document 3). As this kind of microsphere, silica particles are generally most suitable from the viewpoint of chemical resistance and cost.

  When silica particles are used as a seal spacer, for example, after adding silica particles to an uncured material of a thermosetting resin such as an epoxy resin or an acrylic resin and uniformly dispersing it, screen printing, a dispenser, etc. The silica particles are difficult to disperse in the resin. For example, when screen printing is performed, the nozzles may be clogged with aggregates of silica particles. In addition, if a sealing material with poor dispersion of silica particles is used, the cell gap cannot be kept constant, or silica particles tend to aggregate, so the fluidity as a powder is poor and the weighing when used as a seal spacer There was a problem that workability of was bad.

On the other hand, Patent Document 4 discloses that silica particles are treated with alcohol so that the silica particles do not aggregate with each other.
JP 2004-252072 A JP-A-2005-107310 Japanese Patent Laid-Open No. 7-10523 JP-A-9-295807

  The silica particles disclosed in Patent Document 4 are certainly less likely to agglomerate than commonly used silica particles, but they still tend to agglomerate when stored for a long period of time and are not easily dispersed uniformly in the resin. However, there was a problem that the fluidity of the powder deteriorated.

  An object of the present invention is to provide silica particles that can be easily dispersed in a resin without agglomeration even when stored for a long period of time and do not deteriorate in fluidity as a powder.

  As a result of various studies, the present inventors have found that when there are few hydroxyl groups present on the surface of the silica particles, the effect of suppressing aggregation and the effect of improving fluidity do not last long even if treated with alcohol, It has been found that increasing the number of hydroxyl groups on the surface of silica particles makes it difficult to agglomerate for a long period after alcohol treatment and that good fluidity can be maintained even if stored for a long period of time. .

That is, the silica particles of the present invention, in the dry state, the maximum absorbance of 1000～1050Cm ^-1 when measured with FT-IR spectra in diffuse reflection method A _S, the maximum absorbance of 3640～3690Cm ^-1 and A _O when, a _O / a _S is equal to or is from 0.04 to 0.7.

Silica particles of the present invention, the ratio of the maximum absorbance A _O of 3640～3690Cm ^-1 corresponding to expansion and contraction of the hydroxyl groups present on the surface of the maximum absorbance A _S of 1000～1050Cm ^-1 corresponding to expansion and contraction of the Si-O-Si , i.e. for (a _O / a _S) is 0.04 to 0.7, the silica particles hardly agglomerate over a long period of time when alcohol treatment, can be easily dispersed in the resin.

  Moreover, the silica particle which performed the alcohol process can maintain favorable fluidity | liquidity over a long period of time.

A _O / A _S of the silica particles is smaller and the number of hydroxyl groups of the silica particle surface is small it is difficult to suppress aggregation for a long period of time even after the alcohol treatment than 0.04, greater than 0.7 Dehydration condensation reaction is likely to occur from the two hydroxyl groups adjacent to each other, and on the contrary, aggregation is likely to occur. The preferred range of A _O / A _S is from 0.05 to 0.6, furthermore preferably 0.07 to 0.5.

  Such silica particles are obtained by hydrolyzing tetraalkoxysilane or organotrialkoxysilane under alkaline conditions and dehydrating condensation polymerization, and then heat-treating the solid content at 250 to 600 ° C, preferably 350 to 500 ° C. Produced.

  When the silica particles of the present invention are surface-treated with a polar organic solvent after the heat treatment, the surface of the silica particles having a hydroxyl group is protected and higher dispersibility can be maintained. Therefore, even if it is stored for a long period of time or in a humid environment, the hydroxyl groups on the surfaces of the silica particles are less likely to undergo a dehydration condensation reaction, and the hydrogen via water molecules on the surfaces of the silica particles Since it becomes difficult to raise | generate a coupling | bonding, it becomes difficult to aggregate. As the polar organic solvent, alcohols such as methanol, ethanol, isopropanol and n-butanol, carbonyl compounds such as acetone and ethyl methyl ketone, dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and the like can be used.

  The silica particles of the present invention are suitable as a cell gap spacer of a liquid crystal display by treating with an organic solvent as described above and taking advantage of excellent dispersibility, but have various functional groups because of having an appropriate amount of hydroxyl groups on the surface. For example, it can also be used for catalyst supports, optical devices, and microdevices.

  For the introduction of the functional group, a silane coupling agent, specifically, aminosilane, epoxy silane, methacryl silane, ureido silane, isocyanate silane or the like can be used.

  The silica particles of the present invention can be used as seal spacers for liquid crystal displays because they are spherical and have an average particle size of 1 to 15 μm, which is about the same as the cell gap. The average particle diameter is preferably 3 to 10 μm, more preferably 4 to 8 μm.

  When the standard deviation of the particle diameter is 0.1 μm or less, the silica particles of the present invention are suitable as a seal spacer for a liquid crystal display because the cell gap is easily kept constant.

  The manufacturing method of the silica particle of this invention is shown below.

  First, pure water and water-soluble alcohol are mixed and stirred. As the alcohol, ethanol, methanol, isopropanol, n-butanol and the like can be used.

  Next, alkoxysilane is added. As the alkoxysilane, methyltrimethoxysilane, methyltriethoxysilane, tetramethoxysilane, tetraethoxysilane or the like can be used. Thereafter, an appropriate amount of ammonia, triethylamine or the like is added to adjust the pH to about 9 to 10.5.

  Subsequently, the solution to which the above reagents are added is held at 0 to 30 ° C. for several to several tens of hours. When silica particles having a desired particle diameter cannot be obtained, small silica particles are used as seeds and are repeated several times as necessary to obtain a desired particle diameter.

  Finally, the obtained silica particles are heat-treated at 250 to 600 ° C., preferably 350 to 500 ° C., to produce the silica particles of the present invention.

  Hereinafter, the present invention will be described in detail using examples and comparative examples.

  Table 1 shows the characteristics of Examples and Comparative Examples.

[Example]
First, 11500 g of pure water and 620 g of n-butanol were poured into a 20 L reaction vessel equipped with a stirrer and mixed uniformly.

  Next, after stirring for 40 minutes in the thermostat set to 28 degreeC, 510 g of methyltrimethoxysilane was dripped in the reaction container using the metering pump.

  Subsequently, after adding 275 g of a 3% by mass aqueous ammonia solution to the reaction vessel, stirring was stopped and the mixture was allowed to stand at 28 ° C. for 16 hours to precipitate a solid content, followed by decantation to remove the supernatant, The precipitate was dried at 60 ° C. for 25 hours.

  The precipitate (powder) was put in an electric furnace and heated from room temperature to 400 ° C., then heat-treated at 400 ° C. for 9 hours, and cooled to 160 ° C.

  The fired product (powder) thus obtained was taken out from the electric furnace, put into ethanol and dispersed, and subjected to ultrasonic treatment for 4 hours.

  Finally, after solid content was precipitated, the supernatant was removed by decantation and dried at 60 ° C. for 25 hours to obtain 200 g of silica particles. The solvent used was of a reagent level purity.

[Comparative Example 1]
In the electric furnace, the precipitate (powder) was heated from room temperature to 900 ° C., heat-treated at 900 ° C. for 9 hours, and cooled to 160 ° C. to produce silica particles in the same manner as in Example, and 200 g of silica. Particles were obtained.

[Comparative Example 2]
First, 7050 g of methyl alcohol, 4520 g of 25% ammonia aqueous solution and 880 g of pure water were poured into a 20 liter reaction vessel equipped with a stirrer and mixed uniformly.

  Next, the reaction vessel was placed in a thermostat at 30 ° C., and 3130 g of tetraethoxylane was dropped into the reaction vessel using a metering pump. Aging reaction is carried out for 6 hours or more at 30 ° C. after the addition to form the above silica seed particles, and then ammonia and methyl alcohol are removed by a rotary evaporator to obtain an aqueous dispersion of silica seed particles. It was.

  Next, 1040 g of the above silica seed particle aqueous dispersion (370 g of silica content) is put into a 20 liter reaction vessel equipped with a stirrer, and 8540 g of methyl alcohol, 5440 g of 25% aqueous ammonia solution and 780 g of pure water are added. Added and mixed uniformly. Next, 1470 g of tetraethoxylane was dropped into the reaction vessel using a metering pump in a thermostatic chamber at 30 ° C. The silica seed particles were grown by stirring at 30 ° C. for 6 hours or more after the addition. After the solid content was precipitated, the supernatant was removed by decantation.

  Further, 9450 g of methyl alcohol, 5570 g of 25% aqueous ammonia solution and 1290 g of pure water were poured into the reaction vessel and mixed uniformly.

  Next, after stirring the reaction vessel in a thermostat at 30 ° C. for 20 minutes, 1050 g of tetraethoxylane was dropped into the reaction vessel using a metering pump. After the addition, the aging reaction is continued for 6 hours or more at 30 ° C. to grow the particle size of the silica particles. Thereafter, ammonia and methyl alcohol are removed by a rotary evaporator, and the silica particles grown as a particle and the by-product are removed. An aqueous dispersion with fine silica particles was obtained. By repeating sedimentation and decantation of the aqueous dispersion, fine silica particles by-produced were removed to obtain an aqueous dispersion of silica particles.

  Subsequently, the supernatant was removed by decantation, and the precipitate was dried at 60 ° C. for 25 hours.

  This precipitate (powder) was put into an electric furnace, heated from room temperature to 800 ° C., then heat-treated at 800 ° C. for 9 hours, and cooled to 160 ° C.

  The fired product (powder) thus obtained was taken out from the electric furnace, put into ethanol and dispersed, and subjected to ultrasonic treatment for 4 hours.

  After the solid content was precipitated, the supernatant was removed by decantation and dried at 60 ° C. for 25 hours to obtain 500 g of silica particles.

As apparent from Table 1, silica particles embodiments, A _O / A _S is as large as 0.33, it was excellent in dispersibility.

On the other hand, the silica particles of Comparative Examples 1 and 2 both had a small A _O / A _S of 0.03 and poor dispersibility.

  In addition, the average particle diameter in a table | surface calculated | required by measuring the particle diameter of 100 silica particles using the electron microscope (5000 times magnification), and computed the standard deviation.

For A _S and A _O , a sample was mounted on a diffuse reflection measurement unit, and absorbance was measured using FT-IR (Speckin GX manufactured by PerkinElmer), and the maximum absorbance in each wavenumber region was read from the obtained spectrum. The sample used was a mixture of 0.33 g KBr dried at 150 ° C. for 3 hours and 0.01 g silica particles in an agate mortar. The above KBr was used for background measurement.

  For the difficulty of aggregation, that is, dispersibility, 100 g of epoxy resin (World Rock manufactured by Kyoritsu Chemical Industry Co., Ltd.) was charged with 0.5 g of silica particles (those left in an environment of 60 ° C. and 80% humidity for 7 days). When stirring with a propeller stirrer for 5 minutes at 20 rpm, the uniform dispersion was evaluated as “◯” and the case where aggregation was observed was evaluated as “X”.

  The silica particles of the present invention can be suitably used as a spacer for a liquid crystal display panel, but can also be used for a catalyst carrier, an optical device, a microdevice, and the like.

Claims (4)

In the dry state, the maximum absorbance A _S of 1000～1050Cm ^-1 when measured with FT-IR spectra in diffuse reflection method, when the maximum absorbance 3640～3690Cm ^-1 and A _O, A _O / A _S is Silica particles characterized by being 0.04 to 0.7.   The silica particles according to claim 1, wherein the silica particles have an average particle diameter of 1 to 15 μm and are spherical.   The silica particles according to claim 1 or 2, wherein the standard deviation of the particle diameter is 0.1 µm or less.   The silica particles according to any one of claims 1 to 3, wherein the silica particles are used as a spacer for maintaining a cell gap of a liquid crystal display.